Never heard of such a thing. But the name was too cool not to have it, so I made one up instead.
I'm torn. On the one hand, it's kind of an awesome "WTF is this!" monster which can be fun now and then. Good job. But it is kind of goofy. Not duckbunny goofy, but still.
Of course I guess I accept ettins or floating beachballs that disintegrate you by looking at you so maybe I will file it for some future campaign. Two-head (or more) on dogs are quite common, I guess Cerberus had to come from somewhere.